The present invention relates to a process for the preparation of coated seeds.
The majority of cultivation methods give a very uncertain yield. Thus, if the seeds are sown directly in the fields, premature germination takes place before the average ambient humidity is sufficient to ensure the normal growth of the young plants, and this causes significant reductions in the yields. This phenomenon is particularly pronounced in the case of poorly protected seeds, in particular those having an exposed germ.
In order to improve the yield, it is possible to resort to transplanting techniques. In this case, vigorous and well-developed young plants are used and provision is made for the longest possible growth times. To achieve these objectives, the seeds are sown prematurely and the optimum conditions of temperature and humidity level, making it possible to obtain rapid and concomitant germination of the seeds, are selected. However, these techniques are generally uneconomic and only rarely enable quantitative yields to be obtained, either because the seeds do not germinate or because some of the seeds germinate late.
Furthermore, during storage of the seeds, significant losses occur which are generally due to an excessively high ambient humidity or to poor aeration of the silos.
A known technique for improving the germination levels of certain seeds, or for giving them a shape and dimensions suitable for mechanical sowing, consists in coating them with various types of coating agents. Thus, in order to improve the germinating ability of beetroot seeds (Belgian Pat. No. 859,566, filed on Oct. 11, 1977 in the name of the Applicant Company), it has been proposed to incorporate calcium peroxide in the coating agent. This technique, which has proved effective, cannot be directly applied to other seeds of uniform shapes, in particular because the coating agent does not adhere adequately to the seed.
This lack of adhesion is particularly pronounced in the case of poorly protected seeds.
In fact, during coating, a substantial swelling of certain seeds, due to the absorption of water, is frequently observed. After drying, the seed contracts and returns to its initial size, whereas the coating agent does not generally contract in the same proportions; therefore, it does not adhere adequately to the seed and it becomes fragile or splits off. In certain cases, it is difficult correctly to dry the seed under the layer of coating agent, and this entails risks of degradation during storage. These effects are particularly pronounced when the seeds used are leguminosae, maize and cruciferae seeds. Moreover, some coating agents, which on the whole possess valuable properties, can have secondary phytotoxic effects on certain seeds. Finally, in certain cases, it is difficult to coat the seeds in a uniform manner because their surfaces are uneven and do not permit uniform attachment of the coating agents.